Generally, a water pump circulates coolant of a water-cooled engine such as an engine for an automobile. Such a water pump has a casing (which is also referred to a body). The casing is formed by butting a case against a cover, and an impeller is disposed in the interior space of the casing. The water pump rotates the impeller, to draw a coolant from a radiator into the casing and cause the coolant to flow out to an engine outside the casing (Patent Document 1).
As shown in FIGS. 6 and 7, there is a casing that has a partition wall 103 inside a case 100. The partition wall 103 partitions the case 100 into an upstream chamber 101, which is coupled to a radiator, and a downstream chamber 102, in which an impeller is disposed. The partition wall 103 is formed so as to have an approximately same height as that of the tip of impeller 400, so that a coolant radially emitted by the rotation of the impeller 400 does not disturb the flow of a coolant drawn from the side of the upstream chamber 101. The components of the water pump are omitted in FIG. 6.
Attaching the cover 200 in such a manner as to block the upper opening of the case 100 causes the upstream chamber 101 and the downstream chamber 102 on the side of the case 100 to be communicated inside the cover 200, causes the coolant drawn into the upstream chamber 101 in the casing by the rotation of the impeller to flow through the interior of the cover 200 across the partition wall 103 into the downstream chamber 102, and causes the coolant to flow out from the downstream chamber 102 outside the casing.
A laminated gasket 300 is used to seal between the case 100 and the cover 200 water-tightly. In the laminated gasket 300, two gaskets 301 and 301 each having beads and a center plate 302 made of a metal sheet interposed between the gaskets 301 and 301 are laminated. The fastening of the case 100 and the cover 200 with bolts (not shown) compresses the beads, and the reaction forces of the beads at this time seal the laminated gasket 300 between the case 100 and the cover 200.